In order to achieve miniaturization without degrading Q of a dielectric filter in the present invention, resonant elements has upper and lower ground electrodes. The upper ground electrode is formed of upper ground electrodes which correspond to wide portions and have no pattern formed on a portion corresponding to narrow portions, and an upper ground electrode which corresponds to the narrow portions and formed higher than the layer of the upper ground electrodes. The lower ground electrode is formed of lower ground electrodes which correspond to the wide portions and have no pattern formed on a portion corresponding to the narrow portions, and a lower ground electrode which corresponds to the narrow portions and formed lower than the layer of the ground electrodes.
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1. A dielectric filter comprising a dielectric multilayered substrate having an upper surface and a lower surface when the filter is in a horizontal position, comprising:
first and second resonant elements in an inner layer of the substrate, each comprising:
an open end and a grounded end;
a wide portion at the open end for electromagnetically coupling the first and second resonant elements with each other, and
a narrow portion at the grounded end;
first and second input/output electrodes located entirely above the wide portions;
a first upper ground electrode in a layer above the input/output electrodes;
said first upper ground electrode located above said wide portions of the resonant elements, and not located above said narrow portions of the resonant elements, and being above substantially all of the surface area of said wide portions;
a second upper ground electrode in a layer above said first upper ground electrode, said second upper ground electrode located above substantially only said narrow portions of the resonant elements,
a first lower ground electrode in a layer below said first and second resonant elements, said first lower ground electrode located below said wide portions of the resonant elements and not located below said narrow portions of the resonant elements, and being below substantially all of the surface area of said wide portions; and
a second lower ground electrode in a layer below said first lower ground electrode and located below substantially only said narrow portions of the resonant elements.
2. The dielectric filter according to
3. The dielectric filter according to
4. The dielectric filter according to
5. The dielectric filter according to
6. The dielectric filter according to
wherein the second part is perpendicular to the first part and arranged in an opposite direction along a straight line from the second part of the narrow portion of the other resonant element.
7. The dielectric filter according to
8. The dielectric filter according to
9. The dielectric filter according to
10. The dielectric filter according to
11. The dielectric filter according to
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The present invention relates to a dielectric filter used for a high frequency apparatus and the like.
A conventional dielectric filter will be described below.
The dielectric filter is constituted of first and second resonant elements 2 and 3 each of which is formed in the inner layer of a dielectric substrate 1 and has one open end and the other end connected to the ground, wide portions 2b and 3b which electromagnetically couple the first and second resonant elements 2 and 3 with each other and are formed on the sides of open ends 2a and 3a, narrow portions 2c and 3c formed on the side of a side electrode (a common ground terminal, i.e., the ground) 12 of the first and second resonant elements 2 and 3, bent portions 2d and 3d bent like letter L from the ends of the wide portions 2b and 3b to the side electrode 12, first and second input/output electrodes 4a and 5a formed in the upper layer of the bent portions 2d and 3d, input/output terminals 4b and 5b drawn from the input/output electrodes 4a and 5a, a capacitive electrode 11 formed in the upper layer of the wide portions 2b and 3b, an upper ground electrode 6 which is formed in the upper layer of the input/output electrodes 4a and 5a and connected to the side electrode 12, and a lower ground electrode 7 which is formed in the lower layer of the first and second resonant elements 2 and 3 and connected to the side electrode 12.
Ground patterns are formed over the upper ground electrode 6 and the lower ground electrode 7. A distance 8 between the electrode 6 and the wide portions 2b and 3b and a distance 8 between the electrode 6 and the narrow portions 2c and 3c are equal to each other. A distance 9 between the lower ground electrode 7 and the wide portions 2b and 3b and a distance 9 between the lower ground electrode 7 and the narrow portions 2c and 3c are equal to each other.
The input/output terminals 4b and 5b are drawn to the layer of the upper ground electrode 6 through inner vias 4c and 5c. Further, spaces 10a and 10b are provided between the input/output terminals 4b and 5b and the end face of the upper ground electrode 6. The spaces 10a and 10b of 150 μm or larger are necessary to prevent a short circuit on the input/output terminals 4b and 5b when the upper ground electrode 6 formed with a large pattern spreads during screen printing. The input/output terminals 4b and 5b are circular when viewed from the top. The input/output terminals 4b and 5b are about 200 μm in diameter. The dielectric filter protrudes by about 700 μm ((200 μm+150 μm)×2) in the lateral direction of
As indicated by dotted lines in
Similarly, the inductance 24 and the capacitance 25 are connected in parallel to form a parallel connection body 33. The parallel connection body 33 has one end connected to the input/output terminal 5b via the capacitance 26 and the other end connected to the ground. A parallel connection body of the capacitance 29 and the inductance 30 is connected between one end of the parallel connection body 32 and one end of the parallel connection body 33, so that the parallel connection bodies entirely form a band-pass filter.
To be specific, the narrow-band characteristic 37 is obtained by increasing the distance 13 between the narrow portions 2c and 3c to have loose coupling or increasing the inductance 22 (or 24), and the wide-band characteristic 38 is obtained by reducing the distance 13 between the narrow portions 2c and 3c to have close coupling or reducing the inductance 22 (or 24). For example, Japanese Patent Laid-Open No. 7-142904 is known as prior art document information relating to the invention of this application.
In such a conventional dielectric filter, the upper ground electrode 6 is integrally formed over the upper layer of the input/output electrodes 4a and 5a, and the lower ground electrode 7 is integrally formed over the lower layer of the first and second resonant elements 2 and 3. That is, a distance 8 between the upper ground electrode 6 and the wide portions 2b and 3b and a distance 8 between the upper ground electrode 6 and the narrow portions 2c and 3c are equal to each other. The distance 9 between the lower ground electrode 7 and the wide portions 2b and 3b and the distance 9 between the lower ground electrode 7 and the narrow portions 2c and 3c are equal to each other.
When the areas of the wide portions 2b and 3b are reduced without changing the value of the capacitance 23 (or 25) to reduce the dielectric filter, it is necessary to reduce the distance 8 between the upper ground electrode 6 and the wide portions 2b and 3b and the distance 9 between the lower ground electrode 7 and the wide portions 2b and 3b. However, when the distance 8 between the upper ground electrode 6 and the narrow portions 2c and 3c or the distance 9 between the lower ground electrode 7 and the narrow portions 2c and 3c is reduced, Q of the inductance 22 (or 24) decreases, so that the loss of the pass band of the filter constituted of inductors, that is, an insertion loss increases and Q′ of frequency selectiveness decreases. Therefore, it is not possible to reduce the distance 8 or the distance 9 of the wide portions 2b and 3b and the narrow portions 2c and 3c which are integrally formed. Considering this restriction, it is not possible to reduce the dielectric filter without degrading its characteristics.
Further, since the upper ground electrode 6 has a relatively large pattern and conductive paste spreads during screen printing, it is necessary to make the spaces 10a and 10b larger than ordinary spaces, thereby increasing the protrusions of the input/output terminals 4b and 5b and the area of the filter.
The present invention is devised to solve the conventional problem. An object of the present invention is to provide a dielectric filter which prevents Q degradation of an inductor and achieves miniaturization without increasing a filter insertion loss.
In order to solve the problem, a dielectric filter of the present invention formed of a dielectric multilayered substrate, comprising first and second resonant elements each of which is formed in the inner layer of a dielectric substrate and has one open end and the other end connected to the ground, wide portions which electromagnetically couple the first and second resonant elements with each other and are formed on the sides of the open ends, narrow portions formed on the ground sides of the first and second resonant elements, first and second input/output electrodes formed in the upper layer of the wide portions, a plurality of upper ground electrodes which are formed in the upper layer of the first and second input/output electrodes and connected to the ground, and a plurality of lower ground electrodes which are formed in the lower layer of the first and second resonant elements and connected to the ground, wherein the upper ground electrode is formed of first upper ground electrodes which correspond to the wide portions and have no pattern formed on a portion corresponding to the narrow portions and a second upper ground electrode which corresponds to the narrow portions and formed higher than the layer of the first upper ground electrode, and the lower ground electrode is formed of first lower ground electrodes which correspond to the wide portions and have no pattern formed on a portion corresponding to the narrow portions and a second lower ground electrode which corresponds to the narrow portions and formed lower than the layer of the first lower ground electrode.
A dielectric filter formed of a multilayer substrate, comprising first and second resonant elements each of which is formed in the inner layer of a dielectric substrate and has one open end and the other end connected to the ground, wide portions which electromagnetically couple the first and second resonant element and are formed on the sides of the open ends, narrow portions formed on the ground sides of the first and second resonant elements, first and second input/output electrodes formed in an upper layer of the wide portions, an upper ground electrode which is formed in the upper layer of the first and second input/output electrodes and connected to the ground, and a lower ground electrode which is formed in the lower layer of the first and second resonant elements and connected to the ground, wherein the dielectric filter further comprises a plurality of holes provided at almost regular intervals between the upper ground electrode and lower ground electrode corresponding to the wide portions, the holes being filled with a dielectric having a higher permittivity than the dielectric substrate, and a plurality of holes provided at almost regular intervals between the upper ground electrode and lower ground electrode corresponding the narrow portions, the holes being filled with a dielectric having a lower permittivity than the dielectric substrate.
A dielectric filter, comprising a ground electrode provided over a first layer of a dielectric substrate, a resonator electrode which is provided in a second layer of the dielectric substrate and formed of a pattern, and input/output electrodes which are provided in a third layer of the dielectric substrate and is formed of a pattern, wherein the resonator electrode formed in the second layer is formed of first and second resonant elements, each having one open end and the other end connected to the ground, the open ends of the first and second resonant elements are opposed to the input/output electrodes, and the first and second resonant elements have an electromagnetic field influence portion where magnetic field influence is caused by currents passing through the first and second resonant elements and an electromagnetic field non-influence portion where magnetic field influence is not caused by currents passing through the first and second resonant elements.
As described above, according to the present invention, the upper ground electrode of the dielectric filter is formed of the first upper ground electrodes which correspond to the wide portions and have no pattern formed on a portion corresponding to the narrow portions and the second upper ground electrode which corresponds to the narrow portions and formed higher than the layer of the first upper ground electrode, and the lower ground electrode is formed of the first lower ground electrodes which correspond to the wide portions and have no pattern formed on a portion corresponding to the narrow portions and the second lower ground electrode which corresponds to the narrow portions and formed lower than the layer of the first lower ground electrode. The first upper ground electrodes are provided in the upper layer of the wide portions via the first and second resonant elements and the first lower ground electrodes are provided directly below the wide portions, so that a distance between the wide portions and the first upper and lower ground electrodes is reduced.
Therefore, it is possible to obtain a necessary capacitance without increasing the sizes of the wide portions, thereby miniaturizing the dielectric filter.
At this point, no pattern is formed on the first upper and lower ground electrodes facing the narrow portions. However, outside the first upper and lower ground electrodes, the second upper and lower ground electrodes are formed so as to face the narrow portions.
Therefore, distances between the narrow portions and the second upper and lower ground electrodes are increased and the Q of the inductance is not degraded.
The ground electrode is divided into the first and second ground electrodes, so that each pattern area is reduced and other signal electrodes can be arranged at narrow intervals, thereby miniaturizing an overall module including the filter.
According to the present invention, the first and second resonant elements have the electromagnetic field influence portion where magnetic field influence is caused by currents passing through the first and second resonant elements and the electromagnetic field non-influence portion where magnetic field influence is not caused by currents passing through the first and second resonant elements. Thus, by changing a ratio of the electromagnetic field influence portion to the electromagnetic field non-influence portion, a degree of electromagnetic coupling can be varied without changing an inductance value.
That is, the first and second resonant elements can have loose coupling without changing an inductance value determining the characteristic of the filter, and thus the first and second resonant elements can be brought close to each other and the dielectric filter can be miniaturized.
Further, with the electromagnetic field influence portion and the electromagnetic field non-influence portion, it is possible to control the waveform of a signal pass characteristic by changing a ratio of the electromagnetic field influence portion to the electromagnetic field non-influence portion, thereby designing the filter more flexibly.
Even when the wide portions are reduced, a ratio to an inductance formed in the narrow portion is not changed and a pass bandwidth is not changed because of small distances between the wide portions and the upper and lower ground electrodes.
Referring to the accompanying drawings, the following will describe preferred embodiments for implementing the present invention.
As shown in
The detail of the constituent elements will be discussed below. The wide portions 52b and 53b and the bent portions 52d and 53d are short and wide, and thus hardly contribute to inductance but only contribute to a capacitance. The first upper ground electrodes 57a and 57b are disposed above the input/output electrodes 54a and 55a and the capacitive electrode 66 but are not disposed above the narrow portions 52c and 53c. That is, the first upper ground electrodes 57a and 57b are not formed above the narrow portions 52c and 53c. The second upper ground electrode 58 provided in the upper layer of the first upper ground electrode 57 is formed only above the narrow portions 52c and 53c. The second upper ground electrode 58 and the first upper ground electrode 57 are connected to each other via inner vias 59.
Similarly, the first lower ground electrode 60 is disposed below the wide portions 52b and 53b and the bent portions 52d and 53d but is not disposed below the narrow portions 52c and 53c. That is, the first lower ground electrode 60 is not formed below the narrow portions 52c and 53c. The second lower ground electrode 61 disposed in the lower layer of the first lower ground electrode 60 is formed only below the narrow portions 52c and 53c. The second lower ground electrode 61 and the first lower ground electrode 60 are connected to each other via inner vias 62. The first upper ground electrode 57 and the first lower ground electrode 60 are connected to each other via inner vias 63.
In this way, the first upper ground electrode 57 is disposed in the upper layer of the wide portions 52b an 53b and the bent portions 52d and 53d via the input/output electrodes 54a and 55a, and the first lower ground electrode 60 is disposed directly below the wide portions 52b and 53b and the bent portions 52d and 53d, thereby reducing a distance from the wide portions 52b and 53b and the bent portions 52d and 53d to the first upper ground electrode 57. A distance to the first lower ground electrode 60 is also reduced. Since an electric capacitance to the ground can be increased, a necessary capacitance can be obtained without increasing the sizes of the wide portions 52b and 53b and the bent portions 52d and 53d, thereby reducing the size of the dielectric filter. At this point, no pattern is formed on the first upper and lower ground electrodes 57 and 60 facing the narrow portions 52c and 53c. However, outside the upper and lower ground electrodes 57 and 60, the second upper and lower ground electrodes 58 and 61 are formed so as to face the narrow portions 52c and 53c. Therefore, distances between the narrow portions 52c and 53c and the second upper and lower ground electrodes 58 and 61 are increased and the Q of the inductance is not degraded.
Even when the wide portions 52b and 53b are reduced in size, an electric capacitance does not change because the distances between the wide portions 52b and 53b and the upper and lower ground electrodes 57 and 60 are reduced. No change is made to a ratio of an inductance formed on the narrow portions 52c and 53c to a capacitance formed between the wide portions 52b and 53b and the upper and lower ground electrodes 57 and 60, and thus a signal pass characteristic is not changed.
As shown in
The first upper ground layer 57 is divided into three of the ground electrode 57a corresponding to the input/output electrode 54a, the ground electrode 57b facing the input/output electrode 55a, and the second upper ground electrode 58. Similarly, the first lower ground layer 60 is divided into three of the ground electrode 60a facing the wide portion 52b and the bent portion 52d, the ground electrode 60b facing the wide portion 53b and the bent portion 53d, and the second lower ground electrode 61. In this way, the ground electrodes are each divided into three, and thus it is possible to reduce the ground pattern of a layer where the ground electrode is formed.
Further, an upper layer 67a of the first upper ground electrode 57 and a lower layer 67b of the first lower ground electrode 60 are vacant spaces where other electronic circuits can be disposed. Thus, the dielectric filter can be entirely miniaturized. For example, when the dielectric filter of the present embodiment is embedded as a module in a parent substrate, the vacant spaces are used to mount other circuits, so that the parent substrate can be entirely miniaturized.
As shown in
A larger pattern causes the wide spread of the pattern during screen printing. In the present embodiment, the pattern is divided into three, thereby reducing the spread of the pattern. The provision of solder balls on the input/output terminals 54b and 55b achieves a surface mountable dielectric filter.
As indicated by dotted lines in
In
Similarly, the inductance 74 and the capacitance 75 are connected in parallel to form a parallel connection body 83. The parallel connection body 83 has one end connected to the input/output terminal 55b via the capacitance 76 and the other end connected to the ground.
A parallel connection body of the capacitance 79 and the inductance 80 is connected between the one end of the parallel connection body 82 and the one end of the parallel connection body 83, so that the parallel connection bodies form a band-pass filter.
Referring to
Between a side electrode 64 and wide portions 52b and 53b of resonant elements 52 and 53, first narrow portions 52c and 53c and second narrow portions 52e and 53e are formed. Of these narrow portions, the first narrow portions 52c and 53c on the side of the wide portions 52b and 53b are formed in parallel and form an electromagnetic field influence portion where electromagnetic field influence is caused by currents passing through the resonant elements 52 and 53.
The second narrow portions 52e and 53e which are connected with the first narrow portions 52c and 53c and provided inside the side electrode 64 are bent at right angles in opposite directions and connected to the side electrode 64. The second narrow portions 52e and 53e are disposed on a straight line and are not arranged in parallel, and thus the second narrow portions 52e and 53e form an electromagnetic field non-influence portion where magnetic field influence is not caused by currents passing through the resonant elements 52 and 53.
The resonant elements 52 and 53 are not electromagnetically coupled to each other. That is, the resonant elements 52 and 53 form the electromagnetic field non-influence portion. In this case, the first narrow portions 52c and 53c are equal in length. Further, the second narrow portions 52e and 53e are equal in length.
As described above, the electromagnetic field influence portion and the electromagnetic field non-influence portion are obtained using patterns with a simple configuration, thereby achieving an inexpensive dielectric filter. The dielectric filter can be further miniaturized by bending the second narrow portions 52e and 53e forming the electromagnetic field non-influence portion.
The detail of the operating principles of the electromagnetic field non-influence portion will be described in Embodiment 3. This example is also effective to a configuration where first upper and lower ground electrodes are absent and only second upper and lower ground electrodes are provided over a filter.
Embodiment 2 is different from Embodiment 1 in that two capacitive electrodes 91 and 92 are provided and one ends of the electrodes are directly connected to resonant elements 52 and 53 via inner vias 91a and 92a, respectively. In
In
Also in the present embodiment, a distance 95b between a second upper ground electrode 58 and a narrow portion 52c (or 53c) is larger than a distance 95a between the first upper ground electrode 57 and the wide portion 52b (or 53b). Similarly, a distance 96b between a second lower ground electrode 61 and a narrow portion 52c (or 53c) is larger than a distance 96a between a first lower ground electrode 60 and the wide portion 52b (or 53b). Therefore, as in Embodiment 1, it is possible to increase the electric capacitance of the wide portion 52b (or 53b) and the grounds 57 and 60 without reducing Q of the narrow portion 52c (or 53c). That is, the dielectric filter can be miniaturized.
Referring to
Between a side electrode 64 and wide portions 52b and 53b of resonant elements 52 and 53, first narrow portions 52c and 53c and second narrow portions 52e and 53e are formed. Of these narrow portions, the first narrow portions 52c and 53c on the side of the wide portions 52b and 53b are formed in parallel and form an electromagnetic field influence portion where electromagnetic field influence is caused by currents passing through the resonant elements 52 and 53.
The second narrow portions 52e and 53e which are connected with the first narrow portions 52c and 53c and provided inside the side electrode 64 are bent at right angles in opposite directions and connected to the side electrode 64. The second narrow portions 52e and 53e are disposed on a straight line and are not arranged in parallel, and thus the second narrow portions 52e and 53e form an electromagnetic field non-influence portion where magnetic field influence is not caused by currents passing through the resonant elements 52 and 53.
The resonant elements 52 and 53 are not electromagnetically coupled to each other, that is, the resonant elements 52 and 53 form an electromagnetic field non-influence portion. In this case, the first narrow portions 52c and 53c are equal in length. The second narrow portions 52e and 53e are also equal in length.
As described above, the electromagnetic field influence portion and the electromagnetic field non-influence portion are obtained using patterns with a simple configuration, thereby achieving an inexpensive dielectric filter. The dielectric filter can be miniaturized by bending the second narrow portions 52e and 53e forming the electromagnetic field non-influence portion.
The detail of the operating principles of the electromagnetic field non-influence portion will be described in Embodiment 3.
This example is also effective to a configuration where first upper and lower ground electrodes are absent and only second upper and lower ground electrodes are provided over a filter.
To be specific, as shown in
Wide portions 160b and 161b are formed on the sides of the open ends 160a and 161a of the resonant elements 160 and 161. The wide portions 160b and 161b are opposed to the input/output electrodes 157a and 158a formed of copper or silver patterns in the third layer 156. The input/output electrodes 157a and 158a are respectively connected to input/output terminals 157b and 158b provided on a side of the dielectric filter.
Further, a capacitive electrode 164 is provided which is formed of a copper or silver pattern in the third layer 156 so as to face the wide portions 160b and 161b and are electromagnetically coupled to the wide portions 160b and 161b. Moreover, the third layer 156 has a ground electrode 166 which is connected, between the input/output electrodes 157a and 158a, to the ground electrodes 153 and 159 via a side electrode 165. Therefore, it is possible to improve isolation between the input/output electrodes 157a and 158a.
Narrow portions 160c and 161c are formed between the side electrode 163 and the wide portions 160b and 161b of the resonant elements 160 and 161. In the narrow portions 160c and 161c, first portions 160d and 161d on the sides of the wide portions 160b and 161b are formed in parallel. The resonant elements 160 and 161 are electromagnetically coupled to each other between the first portions 160d and 161d. That is, an electromagnetic field influence portion is formed. The narrow portions 160c and 161c, which are connected with the first portions 160d and 161d and provided inside the side electrode 163, have second portions 160e and 161e bent at right angles in opposite directions and connected to the side electrode 163. The second portions 160e and 161e are provided on a straight line and are not arranged in parallel. Thus, the resonant elements 160 and 161 are not electromagnetically coupled to each other on this portion. That is, an electromagnetic field non-influence portion is formed. In this case, the first portions 160d and 161d are equal in length. The second portions 160e and 161e are also equal in length. As described above, the electromagnetic field influence portion and the electromagnetic field non-influence portion are obtained using patterns with a simple configuration, thereby achieving an inexpensive dielectric filter. The dielectric filter can be miniaturized by bending the second portions 160e and 161e forming the electromagnetic field non-influence portion.
The ground electrodes 153 and 159 are opposed to the wide portions 160b and 161b. Further, a ground electrode 141 (not shown) is provided on the undersurface of the first layer 152 so as to face the narrow portions 160c and 161c. Similarly, a ground electrode 142 is provided on the top surface of a protection layer 151a so as to face the narrow portions 160c and 161c. The ground electrodes 141 and 142 are connected to the ground electrodes 153 and 159 via inner vias. Therefore, as in Embodiments 1 and 2, Q of the narrow portions 160c and 161c is increased and the electric capacitance of the wide portions 160b and 161b and the ground electrodes 153 and 159 is increased. The ground electrodes 153 and 159 are not formed on portions opposed to the narrow portions 160c and 161c. This configuration is similar to those of Embodiments 1 and 2. The dielectric filter is 3.5 mm in length, 3.5 mm in width, and 0.4 mm in thickness.
Similarly, reference numeral 175 denotes an inductance of the narrow portion 161d and reference numeral 176 denotes an inductance of the narrow portion 161e. Reference numeral 177 denotes a capacitance formed between the resonant element 161 and the ground electrodes 153 and 159 and the ground electrode 166. Since the wide portions 160b and 161b are wide and short, the inductances thereof are negligible. In this case, the first portions 160d and 161d are equal in length. The second portions 160e and 161e are also equal in length. Therefore, the inductance 172 and the inductance 175 are equal to each other and the inductance 173 and the inductance 176 are equal to each other. The capacitance 174 and the capacitance 177 are also equal to each other.
Reference numeral 178 denotes a capacitance between the wide portion 160b and the capacitive electrode 164 and reference numeral 179 denotes a capacitance between the capacitive electrode 164 and the wide portion 161b. Reference numeral 180 denotes a capacitance formed between the input/output electrode 158a and the wide portion 161b. Reference numeral 158b denotes the input/output terminal connected to the capacitance 180.
In the present embodiment, the ground electrodes 159 and 142 and the ground electrodes 153 and 141 shield the top surface and undersurface of the dielectric filter at the ground, thereby reducing external influence. The ground electrodes are provided on the top surface and the undersurface of the dielectric filter, thereby increasing an electric capacitance between the ground electrodes and the resonator electrode 155 and contributing to miniaturization.
To be specific, the dielectric filter is constituted of a parallel connection body 185 in which the inductance 183 and the capacitance 174 are connected in parallel, the parallel connection body 185 having one terminal connected to the ground and the other terminal connected to the input/output terminal 157b via the capacitance 171, a parallel connection body 186 in which the inductance 184 and the capacitance 177 are connected in parallel, the parallel connection body 186 having one terminal connected to the ground and the other terminal connected to the input/output terminal 158b via the capacitance 180, and a parallel connection body 187 which is connected between the other terminals of the parallel connection body 185 and the parallel connection body 186 and composed of the inductance 182 and the capacitance 181. The capacitance 181 and the inductance 182 constituting the parallel connection body 187 form a parallel resonant circuit to obtain a notch filter. A band-pass filter for removing a frequency designated by the notch filter has such a configuration.
In this case, the relationship of (Formula 1) is established where Lm represents the inductance 182, L1 represents the first portion 160d (or 161d), Lb represents a second portion 160e (or 161e), and K represents a coupling coefficient indicating inductive coupling.
Lm≈(L1+Lb)2/(K×L1) (Formula 1)
(K<<1)
(Formula 1) indicates that the inductance 182 is proportionate to the square of Lb (that is, the second portions 160e and 161e of the narrow portions 160c and 161c). In other words, even when a distance 167 between the first portions 160d and 161d corresponding to L1 is reduced and inductive coupling is increased, the inductance 182 can be made larger by increasing the second portions 160e and 161e corresponding to Lb. That is, the resonant elements 160 and 161 are bent at right angles to form the second portions 160e and 161e not electromagnetically coupled to each other, so that the inductance 182 can be changed almost independently from inductive coupling. In this way, it is possible to control the magnitude of the inductance and inductive coupling causing electromagnetic coupling, so that even when the distance 167 between the resonant elements 160 and 161 is reduced, loose coupling can be obtained. Therefore, it is possible to achieve a small narrow-band filter.
Further, the relationship of (Formula 2) is established where L2 represents the inductance 183, L1 represents the first portion 160d (or 161d), and Lb represents the second portion 160e (or 161e) as in (Formula 1)
L2≈L1+Lb (Formula 2)
(K<<1)
The inductance 183 is represented as a sum of the first portion 160d (or 161d) and the second portion 160e (or 161e).
On the other hand, the dielectric filter has a passage center frequency proportionate to a factor of the square root of the product of the inductance 183 (or 184) and the capacitance 174 (or 177). In the present embodiment, by changing a ratio of the first portion 160d (or 161d) to the second portion 160e (or 161e), it appears that a coupling coefficient (a degree of inductive coupling) is changed while keeping the inductance 183. Conversely, the inductance 183 can vary without changing inductive coupling. Therefore, it is possible to achieve a small narrow-band filter without changing a signal pass characteristic. Moreover, a wide-band filter and a narrow-band filter can be designed more flexibly.
Reference numeral 194 denotes a notch frequency proportionate to a factor of the square root of the product of the inductance 182 and the capacitance 181.
Embodiment 4 is different from Embodiment 1 in that a permittivity between wide portions 52b and 53b and first upper and lower ground electrodes 57 and 60 is increased and a permittivity between narrow portions 52c and 53c and second upper and lower ground electrodes 58 and 61 is reduced.
To be specific, as shown in
With this configuration, a permittivity relative to the ground electrodes 57 and 60 corresponding to the wide portions 52b and 53b becomes higher than that of the dielectric substrate 51, thereby increasing an electric capacitance formed between the wide portions 52b and 53b and the ground electrodes 57 and 60. That is, it is possible to reduce the wide portions 52b and 53b with the same electric capacitance, thereby miniaturizing the dielectric filter.
A plurality of holes 203 are provided at almost regular intervals between narrow portions 52c and 53c and the second upper and lower ground electrodes 58 and 61. The holes 203 are filled with a dielectric 204 having a lower permittivity than the dielectric substrate 51. It is significant that the holes 203 are closely arranged such that an excessive stress is not applied to the dielectric substrate 51 due to a difference in coefficient of thermal expansion between the dielectric 204 and the dielectric substrate 51. The holes 203 may be placed out of the wide portions 52c and 53c. The hole 203 is equal in diameter to the hole 201.
With this configuration, a permittivity between the ground electrodes 58 and 61 corresponding to the narrow portions 52c and 53c is reduced, thereby reducing the conductor loss of the narrow portions 52c and 53c. That is, it is possible to increase Q of inductances forming the dielectric filter.
By filling the holes 201 with a ferroelectric, it is possible to achieve an active filter in which control oh a DC bias changes a permittivity and a filter characteristic.
Embodiment 5 is similar in concept to Embodiment 4. Embodiment 5 is different from Embodiment 4 in that ground electrodes 205 and 206 are integrally provided. To be specific, as shown in
With this configuration, a permittivity relative to the ground electrodes 205 and 206 corresponding to the wide portions 52b and 53b becomes higher than that of the dielectric substrate 51, thereby increasing an electric capacitance between the wide portions 52b and 53b and the ground electrodes 205 and 206. That is, it is possible to reduce the wide portions 52b and 53b with the same electric capacitance, thereby miniaturizing the dielectric filter. The integrated ground electrodes 205 and 206 facilitate fabrication.
A plurality of holes 203 are provided at almost regular intervals between narrow portions 52c and 53c and the ground electrodes 205 and 206. The holes 203 are filled with a dielectric 204 having a lower permittivity than the dielectric substrate 51. It is significant that the holes 203 are closely arranged such that an excessive stress is not applied to the dielectric substrate 51 due to a difference in coefficient of thermal expansion between the dielectric 204 and the dielectric substrate 51. The holes 203 may be placed out of the narrow portions 52c and 53c. The hole 203 is equal in diameter to the hole 201.
With this configuration, a permittivity relative to the ground electrodes 205 and 206 corresponding to the narrow portions 52c and 53c is reduced, and thus the conductor loss of the narrow portions 52c and 53c can be reduced. That is, it is possible to increase Q of inductances forming the dielectric filter, thereby reducing an insertion loss.
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